Here's a recipe someone just shared:
For the best and softest roast that I've made, I did the following:
cut up onions and put on the bottom of the pan with garlic
add some oil and mix.
Take the roast and coat it with salt and pepper. (the one who gave me this recipe also used ginger- but I didn't try that). You could add whatever other spices that you like and rub it into the meat.
optional: add grape juice to the roast for a sweeter taste but not necessary. The juices from the meet come out when you bake at a low temperature for a long time.
Bake for a few hours - probably about 4-6 hours on about 250 or overnight on 225 - depending on the cut. Play around with the time and temperature that works for you.
If you are freezing it, you can bake it, slice it, put it in the freezer. It freezes very well. And from my experience, it gets even softer when you take it out and warm it.